The paper is focused on impact of different oscillation parameters on surface quality of peritectic steel grades cast into billets 150x150 mm. Hydraulic oscillation used for this purpose was temporarily installed on one strand of the billet caster. Hydraulic oscillation enables, in comparison to ordinary used electromechanical oscillation, flexible set-up of basic parameters of the oscillation cycle (negative strip time and its ratio). Proper oscillation mode is capable to assure regular oscillation marks development, good lubrication in the mould and adequate compression of the solidifying shell. Impact of an oscillation mode providing negative strip time 0.085 s and its ratio -50 % on surface quality of cast billets is compared with standard oscillation mode applied on strands equipped with electromechanical oscillation characterized with variable negative strip time between 0.084 and 0.096 s and fixed negative strip ratio to -14 %.

The paper presents analysis of phase transformation temperatures of 20MnCr5 steel. For calculations of required temperatures, i.e. liquidus temperature (TL) and solidus temperature (TS) was used CompuTherm thermodynamic database. The aim of this paper was the use calculated temperatures from CompuTherm thermodynamic database to design regression equations for calculation of the phase transformation temperatures. From the results it is obvious that in the calculation of individual temperatures, the chemical composition has a significant effect on changes of the values of given temperatures. The resulting temperatures also vary depending on the used calculation method (the Lever method proved to be the most suitable). The mean value of liquidus temperature is 1,508 °C and the solidus temperature is 1,462 °C (using CompuTherm and the Lever method). The range of the two-phase zone region for the average content of elements within the limits of 20MnCr5 steel grade is thus 46 °C. Furthermore, the resulting regression equations are given in the work, determined by regression analysis of 66 possible variants of chemical composition of steel 20MnCr5 phase transformation temperatures calculated for defined chemical compositions by thermodynamic database CompuTherm. These equations can be used in operational conditions for calculations of phase transformations in the limit values of the used chemical composition of a given steel grade. When using a different range of chemical composition, these equations can be used, but without guaranteed results.

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